JP2021152450A - Imaging device, and imaging system - Google Patents

Abstract

To provide an imaging technique capable of measuring the optical characteristics of a subject with higher accuracy.SOLUTION: An image pickup apparatus 4 includes a grating 12d, and has an optical coupling layer 12 for waveguiding light, and an imaging surface arranged under an optical coupling layer, and is equipped with a plurality of photodetectors 10 which are periodically arranged along the imaging surface, when light 5 having a predetermined wavelength and a predetermined incident angle is incident, and p/2≤a≤(b + 0.00881)/0.259 is satisfied, when a coherence length of light is defined as a [μm], a waveguide distance of the light guided in the optical coupling layer along the direction in which the grating has a period is defined as b [μm], and a period that has a plurality of photodetectors is defined as p[μm].SELECTED DRAWING: Figure 2A

Description

The present disclosure relates to an imaging device and an imaging system.

Light is an electromagnetic wave and is characterized by optical properties such as polarization or coherence, as well as wavelength or intensity. For example, Patent Document 1 discloses a photodetector that utilizes light coherence among optical characteristics. In the photodetector, among the optical characteristics of the transmitted light or the reflected light from the subject, the phase difference of the light can be measured without complicated operation.

Patent No. 6044862

The present disclosure provides an imaging technique capable of measuring the optical characteristics of a subject with higher accuracy.

を満たす。 The imaging apparatus according to one aspect of the present disclosure includes a grating, and is arranged under the optical coupling layer and an optical coupling layer that waveguides the light when light of a predetermined wavelength and a predetermined incident angle is incident. A plurality of light detectors having an imaging surface and periodically arranged along the imaging surface, the coherence length of the light is a [μm], and the grating is formed in the optical coupling layer. When the waveguide distance of light that is waveguide along the direction having a period is b [μm] and the period of the plurality of optical detectors is p [μm],

Meet.

According to the image pickup apparatus according to one aspect of the present disclosure, the optical characteristics of the subject can be measured more accurately.

FIG. 1 is a diagram schematically showing an example of an imaging system according to the present embodiment. FIG. 2A is a cross-sectional view schematically showing an example of an imaging device according to the present embodiment. FIG. 2B is a plan view schematically showing an example of the image pickup apparatus according to the present embodiment. FIG. 2C is a diagram schematically showing an example of a pattern of a plurality of light-shielding portions. FIG. 2D is a diagram schematically showing an example of a pattern of a plurality of light-shielding portions. FIG. 3 is a diagram schematically showing an optical path in which light is incident and reaches a plurality of photodetectors in the imaging device according to the present embodiment. FIG. 4 is a diagram schematically showing the relationship between the coherence length and the waveguide distance for the light propagating inside the optical coupling layer. FIG. 5 is a diagram showing a calculation example for explaining the ghost reduction effect. FIG. 6 is a diagram showing the results of plotting the relationship between the coherence length and the waveguide distance. FIG. 7A is a perspective view showing an example of an image pickup apparatus in the present embodiment in the presence of a light-shielding film. FIG. 7B is a cross-sectional view showing an example of an image pickup apparatus in the present embodiment in the presence of a light-shielding film. FIG. 7C is a perspective view showing an example of the image pickup apparatus in the present embodiment in the absence of the light-shielding film. FIG. 7D is a cross-sectional view showing an example of the image pickup apparatus in the present embodiment in the absence of the light-shielding film. FIG. 8 is a diagram schematically showing an example of the evaluation system in this embodiment. FIG. 9 is a diagram showing a detection image when light of TE-polarized light and TM-polarized light is incident. FIG. 10 is a diagram schematically showing a measurement system used for measuring the coherence length. FIG. 11 is a diagram showing the results of plotting the relationship between the optical path length difference and the visibility of the interference image. FIG. 12 is a diagram schematically showing an example of a measurement system. FIG. 13 is a diagram showing the result of plotting the relationship between the distance and the brightness in the detected image. FIG. 14A is a diagram illustrating a principle of acquiring a detected image in a conventional photodetector. FIG. 14B is another diagram illustrating the principle of acquiring a detected image in a conventional photodetector.

(Background to one aspect of this disclosure)
The principle of the conventional photodetector will be described below.

FIG. 14A is a diagram illustrating a principle of acquiring a detected image in the conventional photodetector 1401. In FIG. 14A, in the photodetector 1401, the optical path from the incident light to the photodetector 1404 is schematically shown. Note that FIG. 14A shows the arrangement of orthogonal X-axis, Y-axis, and Z-axis for convenience of explanation. The same applies to the following figures.

The photodetector 1401 includes a light-shielding film 1402, an optical coupling layer 1403, and a plurality of photodetectors 1404.

The plurality of photodetectors 1404 include a plurality of first photodetectors 1404a and a plurality of second photodetectors 1404A. The light-shielding film 1402 includes a plurality of openings 1402a and a plurality of light-shielding portions 1402A. The plurality of first photodetectors 1404a each face a plurality of openings 1402a. The plurality of second photodetectors 1404A each face a plurality of light-shielding portions 1402A.

Inside the optical coupling layer 1403 shown in FIG. 14A, the length of the arrow in the left-right direction schematically represents the length of the waveguide distance of light. The waveguide distance qualitatively means the distance at which the light coupled to the optical coupling layer 1403 can travel in the waveguide direction. The quantitative definition and measurement method of the waveguide distance will be described later.

In the example shown in FIG. 14A, it is assumed that two of the four openings 1402a on the right side are incident with light having a phase 180 degrees different from that of the two on the left side. 180 degrees out of phase means light of opposite phase. In the example shown in FIG. 14A, the broken line located in the center and parallel to the Z direction represents a portion where a phase difference exists. When the waveguide distance is about the distance between the opening 1402a and the light-shielding portion 1402A adjacent thereto, only the light incident on the two adjacent openings 1402a interfere with each other inside the optical coupling layer 1403.

As a result, the light incident on the second opening 1402a from the left and the light incident on the third opening 1402a from the left are in opposite phase, so that they are weakened and incident on the second photodetector 1404A. do. On the other hand, the light incident on the first opening 1402a from the left and the light incident on the second opening 1402a from the left are in phase with each other, so that they are intensified and incident on the second photodetector 1404A. Similarly, since the light incident on the third opening 1402a from the left and the light incident on the fourth opening 1402a from the left are in phase, they are intensified and incident on the second photodetector 1404A. .. As a result, the phase difference of the light incident on the four openings 1402a is converted into the amount of light. A low amount of light is detected by the second photodetector 1404A existing between the second opening 1402a from the left and the third opening 1402a from the left. In other words, the amount of light changes where there is a phase difference. This is the principle of acquiring a detected image as an image showing the phase difference.

In the example shown in FIG. 14A, as described above, the waveguide distance is about the distance between the opening 1402a and the light-shielding portion 1402A adjacent thereto. However, in reality, in the conventional photodetector 1401, the waveguide distance may be longer.

FIG. 14B is another diagram illustrating the principle of acquiring a detected image in the conventional photodetector 1401. As shown in FIG. 14B, in the conventional photodetector 1401, the light incident on a certain opening 1402a is combined in the photocouple layer 1403 and reaches the non-adjacent light-shielding portion 1402A. As described above, the waveguide distance may be longer than the example shown in FIG. 14A. In the example shown in FIG. 14B, the arrows in the optical coupling layer 1403 are arranged so as to be offset in the Z direction in order to prevent complication. The arrow does not mean that the physical position of light propagation is offset in the Z direction.

In the example shown in FIG. 14B, the light incident on the first opening 1402a from the left and the light incident on the third opening 1402a from the left are in opposite phases, so that the light is weakened to detect the second light. It is incident on the vessel 1404A. Similarly, the light incident on the second opening 1402a from the left and the light incident on the fourth opening 1402a from the left weaken each other and enter the second photodetector 1404A. As a result, the amount of light changes not only in the place where the phase difference exists but also in the place adjacent to the phase difference. In the present specification, the change in the amount of light in a place where the phase difference does not originally exist is referred to as "ghost".

The waveguide distance is determined, for example, by the grating depth, pitch, refractive index, film thickness, and number of layers in the optical coupling layer. However, in the configuration of a specific optical coupling layer, even if the waveguide distance is short in calculation, the waveguide distance as calculated is not always obtained in reality due to manufacturing constraints. The constraint is, for example, that the grating cannot be formed deep enough, or that the shape, refractive index and film thickness of the grating vary or vary.

The waveguide distance is also determined by, for example, the polarization direction or wavelength of the light incident on the light detection device 1401. Generally, when TE-polarized light is incident on a grating, the waveguide distance tends to be shorter than that of TM-polarized light. This is because TE-polarized light is more likely to be coupled to and radiated from a waveguide having a grating structure than TM-polarized light. However, in calculation, even if the waveguide distance when the TE-polarized light is incident can be shortened, in the actual shooting environment, the light other than the TE-polarized light may be incident on the image pickup apparatus.

Even if the TE-polarized light is emitted from the light source, if the subject is a medium having optical rotation or scattering property, the light incident on the light detection device 1401 is a component of TM polarization or a component of random polarization. Can include. In this case, if a polarizer is arranged in front of the photodetector 1401, the light incident on the photodetector 1401 can be limited to TE-polarized light. However, the amount of light itself can be reduced.

Based on the above studies, the present inventor has come up with the image pickup apparatus described in the following items.

を満たす。 [First item]
The imaging apparatus according to the first item includes a grating, and is arranged under the optical coupling layer and an optical coupling layer that waveguides the light when light of a predetermined wavelength and a predetermined incident angle is incident. A plurality of light detectors having an imaging surface and periodically arranged along the imaging surface are provided, the coherence length of the light is a [μm], and the grating cycles in the optical coupling layer. When the waveguide distance of the light waveguide along the direction of the light is b [μm] and the period of the plurality of light detectors is p [μm],

Meet.

を満たしてもよい。 [Second item]
The imaging apparatus according to the first item includes a light-shielding film arranged on the optical coupling layer, and the plurality of photodetectors include a plurality of first photodetectors and a plurality of second photodetectors. The light-shielding film includes a plurality of alternately arranged openings and a plurality of light-shielding portions, each of the plurality of openings facing the plurality of first photodetectors, and the plurality of light-shielding portions. Facing the plurality of second photodetectors, respectively,

May be satisfied.

[Third item]
In the imaging apparatus according to the first or second item, the optical coupling layer is arranged on the first low refractive index layer and the first low refractive index layer, and includes the grating. The first high refractive index layer includes the first high refractive index layer and the second low refractive index layer arranged on the first high refractive index layer, and the first high refractive index layer is the first low refractive index layer and the second low refractive index layer. It may have a higher refractive index than the low refractive index layer.

を満たしてもよい。 [Fourth item]
In the imaging apparatus according to any one of the first to third items, the coherence length of the light is

May be satisfied.

を満たしてもよい。 [Fifth item]
In the imaging apparatus according to any one of the first to third items, the coherence length of the light is

May be satisfied.

[Sixth item]
In the image pickup apparatus according to any one of the first to fifth items, the plurality of photodetectors may be arranged two-dimensionally.

[7th item]
In the image pickup apparatus according to any one of the first to sixth items, the light incident on the optical coupling layer may contain a component of TM polarized light.

[8th item]
The imaging system according to the eighth item includes the imaging device according to any one of claims 1 to 7, and a light source that emits the light having a coherence length a.

The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions of the components, etc. shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components.

In the present disclosure, all or part of a circuit, unit, device, member or part, or all or part of a functional block in a block diagram, refers to a semiconductor device, a semiconductor integrated circuit (IC), or an LSI (range scale integration). It may be executed by one or more electronic circuits including. The LSI or IC may be integrated on one chip, or may be configured by combining a plurality of chips. For example, functional blocks other than the storage element may be integrated on one chip. Here, it is called LSI or IC, but the name changes depending on the degree of integration, and it may be called system LSI, VLSI (very large scale integration), or ULSI (ultra large scale integration). A Field Programmable Gate Array (FPGA), which is programmed after the LSI is manufactured, or a reconfigurable logistic device that can reconfigure the junction relationship inside the LSI or set up the circuit partition inside the LSI can also be used for the same purpose.

Further, all or part of the functions or operations of circuits, units, devices, members or parts can be performed by software processing. In this case, the software is recorded on a non-temporary recording medium such as one or more ROMs, optical discs, hard disk drives, and is identified by the software when it is executed by a processor. Functions are performed by the processor and peripherals. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and the required hardware device, such as an interface.

Hereinafter, embodiments will be specifically described with reference to the drawings.

(Structure of Embodiment)
FIG. 1 is a diagram schematically showing an example of an imaging system 100 in this embodiment. The image pickup system 100 includes a light source 1, a subject 2, a lens optical system 3, and an image pickup device 4.

The light source 1 emits light having a constant coherence length to the subject 2. Let a be the coherence length of the light. The quantitative definition and measurement method of the coherence length a will be described later.

The light source 1 may continuously emit light of a constant intensity. The light source 1 may emit pulsed light having a spatial pulse width sufficiently longer than the coherence length a. The wavelength of the light emitted from the light source 1 is arbitrary. When the subject 2 is a living body, the wavelength of the light source 1 can be set to, for example, about 650 nm or more and about 950 nm or less. This wavelength range is included in the wavelength range from red to near infrared rays. In this specification, the term "light" is used not only for visible light but also for infrared light.

The lens optical system 3 is, for example, a condenser lens or a telecentric lens. The lens optical system 3 collects the light emitted from the light source 1 and transmitted through the subject 2. The arrangement of the light source 1, the subject 2, and the lens optical system 3 is not limited to the example shown in FIG. The lens optical system 3 may be arranged so as to collect the light emitted from the light source 1 and reflected by the subject 2. The lens optical system 3 may be arranged so as to emit light emitted from the light source 1, scatter inside the subject 2, and collect the light emitted from the surface of the subject 2.

The focused light is imaged at the image plane position of the lens optical system 3. The lens optical system 3 shown in FIG. 1 includes one lens, but may include a plurality of lenses.

The image pickup apparatus 4 is arranged at the image plane position of the lens optical system 3.

2A and 2B are a cross-sectional view and a plan view schematically showing an example of the image pickup apparatus 4 in the present embodiment, respectively. The cross-sectional view shown in FIG. 2A is a cross-sectional view in the XZ plane along the direction in which light is incident. The cross section includes a region surrounded by a broken line shown in FIG. 2B. The plan view shown in FIG. 2B is a plan view of the image pickup apparatus 4 in the XY plane when viewed from the side where the light is incident. The plan view includes a light-shielding film 9 described later. With the cross-sectional structure shown in FIG. 2A as one unit structure, a plurality of unit structures are periodically arranged in the XY plane.

The image pickup apparatus 4 includes a plurality of photodetectors 10, an optical coupling layer 12, and a light-shielding film 9 in this order. In the example shown in FIG. 2A, a plurality of photodetectors 10, an optical coupling layer 12, and a light-shielding film 9 are laminated in the Z direction. In the example shown in FIG. 2A, the transparent substrate 9b and the bandpass filter 9p are arranged in this order on the light-shielding film 9.

The plurality of photodetectors 10 are periodically arranged along the XY plane under the photocouple layer 12. The plurality of photodetectors 10 include a plurality of first photodetectors 10a and a plurality of second photodetectors 10A in the XY plane. The XY plane may be referred to as an "imaging plane". It can be said that the plurality of photodetectors 10 have an imaging surface.

The plurality of photodetectors 10 include a plurality of first microlenses 11a and a plurality of second microlenses 11A arranged in an XY plane, a transparent film 10c, and a metal such as a wiring from the side where light is incident. It includes a film 10d and a plurality of photosensitive parts formed of Si, an organic film, or the like. Each of the plurality of photosensitive members is arranged between two metal films 10d adjacent to each other in the X direction or the Y direction. The plurality of photosensitive members correspond to the plurality of first photodetectors 10a and the plurality of second photodetectors 10A. The plurality of first microlenses 11a are arranged so as to face each of the plurality of first photodetectors 10a. Similarly, the plurality of second microlenses 11A are arranged so as to face each of the plurality of second photodetectors 10A. The light collected by the first microlens 11a and incident on the gap between the two adjacent metal films 10d is detected by the first photodetector 10a. Similarly, the light collected by the second microlens 11A and incident on the gap between the two adjacent metal films 10d is detected by the second photodetector 10A.

Let p be the arrangement period of the plurality of photodetectors 10. The plurality of photodetectors 10 have an arrangement period at least in the waveguide direction of light in the optical coupling layer 12. In the example shown in FIG. 2A, the waveguide direction of light is the X direction. The plurality of photodetectors 10 need not be arranged periodically except in the waveguide direction.

The optical coupling layer 12 includes a grating 12d and guides light when light having a predetermined wavelength and a predetermined angle of incidence is incident. The configuration of the optical coupling layer 12 is as follows. The optical coupling layer 12 is arranged on a plurality of photodetectors 10. The optical coupling layer 12 includes a low refractive index transparent layer 12c, a high refractive index transparent layer 12b, and a low refractive index transparent layer 12a in this order in the direction perpendicular to the plane of the light detector 10. The high refractive index transparent layer 12b is arranged on the low refractive index transparent layer 12c. The high refractive index transparent layer 12b includes a grating 12d. The high refractive index transparent layer 12b has a higher refractive index than the low refractive index transparent layer 12c and the low refractive index transparent layer 12a. The low refractive index transparent layer 12c and the low refractive index transparent layer 12a are formed of _{, for example, SiO 2.} The high refractive index transparent layer 12b is formed from _{, for example, Ta 2} O _5.

The optical coupling layer 12 may have a structure in which the high refractive index transparent layer 12b and the low refractive index transparent layer 12c are further repeated in this order. In the example shown in FIG. 2A, a structure repeated 6 times in total is shown. The high refractive index transparent layer 12b is sandwiched between the low refractive index transparent layer 12a and the low refractive index transparent layer 12c, and functions as a waveguide layer. A linear grating 12d having a pitch of Λ is formed over the entire surface at the interface between the high refractive index transparent layer 12b and the low refractive index transparent layer 12c and the interface between the high refractive index transparent layer 12b and the low refractive index transparent layer 12a. NS. The grating lattice vector is parallel to the X direction in the XY plane of the optical coupling layer 12. The shape of the cross section of the grating 12d in the XZ plane is sequentially transferred to the laminated high refractive index transparent layer 12b and the low refractive index transparent layer 12c. The film formation of the high refractive index transparent layer 12b and the low refractive index transparent layer 12c may have high directivity in the stacking direction. At this time, by making the shape of the cross section of the grating 12d on the XZ plane S-shaped or V-shaped, the transferability of the shape can be easily maintained.

The grating 12d is formed on at least a part of the high refractive index transparent layer 12b. The grating 12d allows the incident light to be coupled to the waveguide light propagating through the high refractive index transparent layer 12b. The incident light is guided in the optical coupling layer 12 along the direction in which the grating 12d has a period Λ.

Let b be the waveguide distance of the optical coupling layer 12 configured as described above. The quantitative definition and measurement method of the waveguide distance b will be described later.

The gap between the optical coupling layer 12 and the photodetector 10 may be, for example, as narrow as possible or may be in close contact with each other. A transparent medium such as an adhesive may be filled in the gap and the space between the microlens 11a and the microlens 11A. When the transparent medium is filled, the microlens 11a and the microlens 11A have a sufficiently larger refractive index than the filled transparent medium in order to obtain the lens effect.

The light-shielding film 9 is arranged on the light-bonding layer 12. The light-shielding film 9 includes a plurality of light-shielding portions 9A alternately arranged in the XY plane of the light-shielding film 9, and a plurality of openings 9a. In the example shown in FIG. 2A, the plurality of light-shielding portions 9A and the plurality of openings 9a are formed by patterning a metal reflective film formed of, for example, Al on a transparent substrate 9b described later.

The opening 9a shown in FIG. 2A corresponds to, for example, the openings 9a1, 9a2, 9a3, 9a4 shown in FIG. 2B. The light-shielding portion 9A shown in FIG. 2A corresponds to, for example, the light-shielding portions 9A1, 9A2, 9A3, 9A4 shown in FIG. 2B. The plurality of light-shielding portions 9A face each of the plurality of second photodetectors 10A. The plurality of openings 9a face each of the plurality of first photodetectors 10a.

In addition, one opening 9a may face two or more first photodetectors 10a. One light-shielding portion 9A may face two or more second photodetectors 10A.

2C and 2D are diagrams schematically showing an example of a pattern of a plurality of light-shielding portions 9A.

The plurality of light-shielding portions 9A form a checker pattern, for example, as shown in FIG. 2B. In addition to the checker pattern, the plurality of light-shielding portions 9A may form a stripe pattern, for example, as shown in FIG. 2C.

The plurality of light-shielding portions 9A may form other patterns. Each of the plurality of light-shielding portions 9A may have a width different from that of the plurality of openings 9a, as shown in FIG. 2D, for example. In the example shown in FIG. 2D, a part of each opening 9a also faces the second photodetector 10A.

In the image pickup apparatus 4, the light-shielding film 9 may not be present. That is, all the regions on the optical coupling layer 12 may be the openings 9a. In this case, the opening 9a faces both the first photodetector 10a and the second photodetector 10A. Regardless of the presence or absence of the light-shielding film 9, the plurality of photodetectors 10 are periodically arranged at least in the waveguide direction of the light in the optical coupling layer 12.

In the example shown in FIGS. 2A to 2D, the plurality of openings 9a, the plurality of light-shielding portions 9A, and the plurality of photodetectors 10 are arranged two-dimensionally, but even if they are arranged one-dimensionally. good.

The transparent substrate 9b is arranged on the light incident side of the light shielding film 9. The transparent substrate 9b is formed of a material such as _{SiO 2.} The bandpass filter 9p is arranged on the light incident side of the transparent substrate 9b. The bandpass filter 9p selectively transmits only the incident light 5 having a wavelength _{near λ 0.}

The incident light 5 passes through the bandpass filter 9p and the transparent substrate 9b, and reaches the light-shielding portion 9A on which the reflective film is formed and the opening 9a from which the reflective film is removed as light 6A and light 6a, respectively. The light 6A is shielded by the light-shielding portion 9A. The light 6a passes through the opening 9a and is incident on the optical coupling layer 12. The light 6a incident on the optical coupling layer 12 is incident on the high refractive index transparent layer 12b via the low refractive index transparent layer 12a. A grating 12d is formed at the upper and lower interfaces of the high refractive index transparent layer 12b. If the following equation (1) is satisfied, the waveguide light 6b is generated.

Here, N is the effective refractive index of the waveguide light 6b, and θ is the incident angle with respect to the normal of the XY plane which is the incident surface. In the example shown in FIG. 2A, the light is incident perpendicularly to the incident surface. Therefore, θ = 0. In this case, the waveguide light 6b propagates in the XY plane in the X direction. That is, the light incident on the optical coupling layer 12 through the opening 9a is guided in the direction of the adjacent light-shielding portion 9A in the X direction.

The light component that passes through the high-refractive-index transparent layer 12b and is incident on the lower layer is also incident on all the high-refractive-index transparent layers 12b on the lower layer side. As a result, the waveguide light 6c is generated under the same conditions as in the equation (1). In the example shown in FIG. 2A, waveguide light is actually generated in all the high refractive index transparent layers 12b. In the example shown in FIG. 2A, for the sake of simplicity, the waveguide light 6b and the waveguide light 6c generated in the two layers are shown as representatives. The waveguide light 6c generated on the lower layer side propagates in the X direction in the XY plane in the same manner as the waveguide light 6b.

The waveguide light 6b and the waveguide light 6c propagate while radiating light in the vertical direction at an angle θ. In the example shown in FIG. 2A, θ = 0. Of the synchrotron radiation 6B1 and the synchrotron radiation 6C1, the component toward the light-shielding portion 9A is reflected by the light-shielding portion 9A and becomes light 6B2 downward along the normal line of the reflection surface of the light-shielding portion 9A in the XY plane. The light 6B1, the light 6C1, and the light 6B2 satisfy the formula (1) in the high refractive index transparent layer 12b. Therefore, a part of the light 6B1, the light 6C1, and the light 6B2 becomes the waveguide light 6b and the waveguide light 6c again. The waveguide light 6b and the waveguide light 6c newly generate synchrotron radiation 6B1 and synchrotron radiation 6C1, respectively. In this way, the same process is repeated. As a whole, immediately below the opening 9a, a component of the incident light that did not become waveguide light passes through the optical coupling layer 12 and enters the microlens 11a as transmitted light 6d, and the first photodetector 10a Detected by. Immediately below the light-shielding portion 9A, a component of the incident light that has become waveguide light is incident on the microlens 11A as synchrotron radiation 6D, and is detected by the second photodetector 10A.

The opening 9a is also a translucent region in the image pickup apparatus 4. The light incident through the opening 9a is branched and detected by the photodetector 10a directly below and the left and right photodetectors 10A adjacent to each other in the X direction.

The plurality of first photodetectors 10a and the plurality of second photodetectors 10A included in the plurality of photodetectors 10 detect the amount of light. The detected light intensity signal is output as a detected image.

Of the plurality of first photodetectors 10a, it is assumed that four photodetectors facing the openings 9a1 to 9a4 shown in FIG. 2B each detect the amount of light from q1 to q4, respectively. Similarly, of the plurality of second photodetectors 10A, it is assumed that four photodetectors facing the light-shielding portions 9A1 to the light-shielding portions 9A4 shown in FIG. 2B each detect the amount of light from Q1 to Q4, respectively. q1 to q4 are the detected light amounts of the light that did not become the waveguide light, and Q1 to Q4 are the detected light amounts of the light that did not become the waveguide light. The photodetector directly below the opening 9a1 does not detect the amount of light that has become waveguide light, and the photodetector directly below the light-shielding portion 9A2 does not detect the amount of light that has not become waveguide light. Here, at the detection position directly below the opening 9a1, the detected light amount of the light that has become waveguide light is defined as Q0 = (Q1 + Q2 + Q3 + Q4) / 4 or Q0 = (Q1 + Q2) / 2. Similarly, at the detection position directly below the light-shielding portion 9A2, the amount of detected light that does not become waveguide light is defined as q0 = (q1 + q2 + q3 + q4) / 4 or q0 = (q1 + q2) / 2. That is, the amount of detected light in a region having the light-shielding portion 9A or the opening 9a is defined as the average value of a plurality of detected light amounts directly under the plurality of regions adjacent to the region in the X direction and / or the Y direction. By applying this definition to all regions, the amount of detected light that did not become waveguide light in all the first photodetector 10a and the second photodetector 10A included in the plurality of photodetectors 10. And the amount of detected light of the light that has become waveguide light can be defined. It is assumed that the detected light amount of the light that has not become the waveguide light and the detected light amount of the light that has become the waveguide light are defined as described above. The value of the ratio of these detected light amounts or the value of the ratio of each detected light amount based on the sum of these detected light amounts is calculated for each photodetector. An image is generated by assigning the calculated value to the pixel corresponding to each photodetector. By the above arithmetic processing, a detected image including information on the spatial distribution of the phase difference can be obtained.

(Operation of the embodiment)
The principle of reducing ghosts in the image pickup apparatus 4 according to the present embodiment will be described below.

FIG. 3 is a diagram schematically showing an optical path in which light is incident and reaches a plurality of photodetectors 10 in the image pickup apparatus 4 of the present embodiment.

In the example shown in FIG. 3, in the optical coupling layer 12, the light incident on the first opening 9a from the left and the light incident on the third opening 9a from the left overlap each other. Similarly, the light incident on the second opening 9a from the left and the light incident on the fourth opening 9a from the left overlap each other.

The difference from the conventional point is that the coherence length a of the incident light 5 is shortly limited with reference to the waveguide distance b in the optical coupling layer 12.

FIG. 4 is a diagram schematically showing the relationship between the coherence length a and the waveguide distance b for the light propagating inside the optical coupling layer 12. The light 41 propagating from the left and the light 42 propagating from the right overlap each other within the range of the waveguide distance b, as shown in the region surrounded by the broken line. However, the coherence length a of the light 41 and the light 42 is shorter than the waveguide distance b. Therefore, a phenomenon occurs in which interference does not occur even though the lights overlap. This is because the lights located farther than the coherence length a do not have a phase correlation with each other.

As a result, in the example shown in FIG. 3, in the optical coupling layer 12, only the light incident on the two openings 9a adjacent to each other interfere with each other. Similar to the example shown in FIG. 14A, the light incident on the second opening 9a from the left and the light incident on the third opening 9a from the left are in opposite phase, so that they are weakened to each other and the second light is weakened. It is incident on the photodetector 10A. On the other hand, the light incident on the first opening 9a from the left and the light incident on the second opening 9a from the left are in phase with each other, so that they are intensified and incident on the second photodetector 10A. Similarly, since the light incident on the third opening 9a from the left and the light incident on the fourth opening 9a from the left are in phase, they are intensified and incident on the second photodetector 10A. .. This reduces ghosting. As a result, the change in the amount of light occurs in the place where the phase difference exists, and the change in the amount of light hardly occurs in the place where the phase difference does not exist.

When the coherence length a is at least half the distance between two adjacent openings 9a, the light incident on the two openings 9a interferes. In the image pickup apparatus 4 in the present embodiment, the distance between two adjacent openings 9a is 2p. Therefore, when the coherence length a of the incident light is p or more, light interference occurs.

In the following, the quantitative relationship between the coherence length a and the waveguide distance b will be described.

FIG. 5 is a diagram showing a calculation example for explaining the ghost reduction effect. The interference characteristics of laser light are represented by changes in the Gaussian curve with distance. The width of the Gaussian curve represents the coherence length a. On the other hand, the waveguide property of the optical coupling layer 12 is represented by an exponential change depending on the distance. This is because the light bound in the optical coupling layer 12 propagates while radiating the light in the Z direction. The degree of attenuation of the guided light is determined by the waveguide distance b.

Therefore, the waveguide characteristic of light having coherence is obtained by multiplying the interference characteristic of laser light by the waveguide characteristic of the optical coupling layer 12. The hatched region shown in FIG. 5 represents a region sandwiched between the waveguide characteristics of the optical coupling layer 12 and the waveguide characteristics of light having coherence. The area of the region represents the ghost reduction rate R. The ghost reduction rate R is a value that quantifies a significantly observable reduction in ghosts.

The distance at which the interference characteristics of the laser beam decrease to 1 / e of the peak value is defined as the coherence length a. The distance at which the intensity of the light to be guided decreases to 1 / e of the peak value is defined as the waveguide distance b. At this time, the ghost reduction rate R is expressed by the following equation (2).

FIG. 6 is a diagram showing the result of plotting the relationship between the coherence length a and the waveguide distance b calculated from the equation (2). In the example shown in FIG. 6, the relationship between a and b when R = 0.1, 0.2, ..., 0.9 is expressed by a straight line equation.

When the ghost reduction rate R is 10% or more, the relationship between a and b is expressed by the following equation (3).

However, for a and b, numerical values when the unit is μm are used. The same applies to the following equation.

Assuming that the ghost reduction rate R is 30% or more in order to obtain a greater effect, the relationship between a and b is expressed by the following equation (4).

Assuming that the ghost reduction rate R is 50% or more in order to obtain a larger effect, the relationship between a and b is expressed by the following equation (5).

Assuming that the ghost reduction rate R is 70% or more in order to obtain a larger effect, the relationship between a and b is expressed by the following equation (6).

Assuming that the ghost reduction rate R is 90% or more in order to obtain a larger effect, the relationship between a and b is expressed by the following equation (7).

Based on the above principle, the image pickup apparatus 4 in the present embodiment has special effects of reducing ghosts appearing in the detected image and measuring the phase difference with higher accuracy.

In the image pickup apparatus 4 of the present embodiment, the openings 9a and the light-shielding portions 9A are alternately arranged in the waveguide direction. On the other hand, even if the light-shielding portion 9A does not exist, the effect of reducing ghost can be obtained.

The image pickup apparatus 4 in the case where the light-shielding film 9 is present and in the case where the light-shielding film 9 is not present will be described below.

7A and 7B are perspective views and cross-sectional views showing an example of the image pickup apparatus 4 in the present embodiment in the presence of the light-shielding film 9, respectively. In the examples shown in FIGS. 7A and 7B, all in-phase light is incident on the opening 9a. When the light-shielding film 9 is present, the minimum distance for causing interference is the arrangement period p of the plurality of photodetectors 10. Assuming that the ghost reduction rate R is 10% or more, the relationship between a, b, and p is expressed by the following equation (8).

7C and 7D are perspective views and cross-sectional views showing an example of the image pickup apparatus 4 in the present embodiment in the absence of the light-shielding film 9, respectively. In the examples shown in FIGS. 7C and 7D, all in-phase light is incident on the opening 9a. Light is guided in the optical coupling layer 12 regardless of the presence or absence of the light-shielding film 9. The difference in the absence of the light-shielding film 9 is that the minimum distance for causing interference is half the p / 2 of the arrangement period of the plurality of photodetectors 10. Assuming that the ghost reduction rate R is 10% or more, the relationship between a, b, and p is expressed by the following equation (9).

Further, if the coherence length a is adjusted as follows, the maximum effect for obtaining a phase difference image while reducing ghosts can be obtained in the image pickup apparatus 4 according to the present embodiment. That is, the coherence length a is adjusted between the minimum distance for causing interference and the minimum distance for which interference is not desired to occur.

When the light-shielding film 9 is present, the minimum distance for causing interference is the distance p from the opening 9a to the adjacent light-shielding portion 9A. The minimum distance at which interference does not occur is the distance 2p from the opening 9a to the adjacent opening 9a. When the coherence length a = 1.5p, which is in the middle of these distances, the maximum effect can be obtained. The same effect can be obtained in the range of 1.4p ≦ a ≦ 1.6p.

In the absence of the light-shielding film 9, the minimum distance for causing interference is half the distance p / 2 from the opening 9a to the adjacent opening 9a. The minimum distance at which interference is not desired to occur is the distance p from the opening 9a to the adjacent opening 9a. When the coherence length a = 0.75p, which is in the middle of these distances, the maximum effect can be obtained. The same effect can be obtained in the range of 0.7p ≦ a ≦ 0.8p.

If the coherence length a in the equations (8) and (9) is divided by the arrangement period p of the plurality of photodetectors 10, the coherence length a is defined by how many times the arrangement period p of the plurality of photodetectors 10 is. You can also do it.

(Example)
Hereinafter, examples carried out to confirm the effects of the present disclosure will be described.

FIG. 8 is a diagram schematically showing an example of the evaluation system in this embodiment. As an evaluation target, an optical element 84 including a light-shielding film 9 and an optical coupling layer 12 was used instead of the image pickup apparatus 4. The light transmitted through the optical element 84 was photographed by a microscope. From the brightness distribution in the captured image, a detected image was obtained by the above-mentioned arithmetic processing.

The width W of the opening 9a and the light-shielding portion 9A in the light-shielding film 9 in the X direction was set to 5.6 μm. The arrangement period p of the plurality of photodetectors 10 was set to 5.6 μm, which is the same value as the width W. The depth of the grating of the optical coupling layer 12 in the Z direction was 0.19 μm, and the pitch was 0.45 μm. The high refractive index transparent layer 12b was a Ta ₂ O ₅ film, and the thickness t1 in the Z direction was 0.34 μm. The low refractive index transparent layer 12a and the low refractive index transparent layer 12c were formed as a SiO ₂ film, and the thickness t2 in the Z direction thereof was 0.22 μm.

As the light source 81, a DFB laser diode having a wavelength of 850 nm was used. The light emitted from the light source 81 was converted into parallel light by a collimator lens (not shown). In the retardation sample 82, a dent was formed in a quartz glass having a thickness of 1 mm by FIB (Focused Ion Beam) processing. The size of the indentation was a rectangle of 90 μm × 56 μm, and the depth was 680 nm. The steepness of the step is about a width of less than one pixel in the image on the optical element 84. When parallel light is emitted so as to straddle the step of the depression, the light transmitted through the phase difference sample 82 becomes light having a steep phase difference with the step as a boundary.

Using a telecentric lens as the lens optical system 83, an image of the retardation sample 82 was formed on the exit surface of the optical coupling layer 12. The waveguide direction of the light incident on the optical coupling layer 12 is the X direction.

The coherence length a of the light emitted from the light source 81 was adjusted by the following method. That is, it is a method in which the drive current of the DFB laser diode is modulated at 600 MHz by a high frequency modulation power supply (not shown), and the upper limit value and the lower limit value of the modulation current are adjusted. In this example, two types of coherence lengths a = 18 mm and a = 26 μm were used. The coherence length a = 18 mm was obtained by a drive current with an upper limit value of 65 mA and a lower limit value of 0 mA. The coherence length a = 26 mm was obtained by a drive current with an upper limit of 58 mA and a lower limit of 0 mA. The method for measuring the coherence length a will be described later. Further, in the case of TM-polarized incident light, the waveguide distance b of the optical coupling layer 12 was 18 μm. The method for measuring the waveguide distance b will be described later.

Using the above evaluation system, detected images for both TE-polarized and TM-polarized incident light were evaluated.

FIG. 9 is a diagram showing a detection image when light of TE-polarized light and TM-polarized light is incident. The above-mentioned arithmetic processing is applied to the detected image. Each detected image is displayed so that the brightness becomes low at a place where a large phase difference is detected. Further, as the amount of light not detected by the photodetector, the average value of the amount of light of the pixels on both sides was used. The average value is Q0 = (Q1 + Q2) / 2, or q0 = (q1 + q2) / 2.

In the detected image, the phase difference in the X direction, which is the waveguide direction, was detected. The phase difference corresponds to the step of the subject.

As shown in FIG. 9, when a TE-polarized light having a coherence length of a = 18 mm or a = 26 μm is incident, or when a TM-polarized light having a coherence length a = 26 μm is incident, a step is mainly present. In, the occurrence of a phase difference has been detected. However, when TM-polarized light having a coherence length of a = 18 mm is incident, it is detected that the phase difference is generated even in the periphery where the phase difference is not originally generated. This is a ghost.

From the example shown in FIG. 9, it can be seen that when the coherence length a = 18 mm, a large amount of ghosts are generated especially when TM-polarized light is incident. This is because a = 18 mm does not satisfy the above-mentioned equation (8).

On the other hand, when the coherence length a = 26 μm is shortened, it can be seen that even when TM-polarized light is incident, the ghost is reduced as compared with the case where the coherence length a = 18 mm. It can be seen that the coherence length a = 26 μm satisfies the above-mentioned equation (8).

As described above, from the present embodiment, it can be seen that the image pickup apparatus 4 in the present embodiment has special effects of reducing ghosts appearing in the detected image and measuring the phase difference with higher accuracy. Even if the incident light contains a TM polarized component, a special effect can be obtained.

In this embodiment, the coherence length a was fixed to a specific value, and a detected image was acquired. On the other hand, the coherence length a may be adjusted within the range of the above equation (8) with reference to the waveguide distance b to acquire a plurality of different detection images. In this case, more detailed optical characteristics of the subject can be obtained from the plurality of detected images.

(Measuring method of coherence length)
Hereinafter, an example of a method for measuring the coherence length a will be described.

FIG. 10 is a diagram schematically showing a measurement system used for measuring the coherence length a. The measurement system is a so-called Michelson interferometer. The light emitted from the light source 1001 is branched by the half mirror 1006. The light of the two branched optical paths is reflected by the mirror 1005a and the mirror 1005b, respectively, and then combined again by the half mirror 1006. As a result, an interference image is obtained. An interference image is observed by the camera 1004 while moving one of the mirrors 1005a in the optical axis direction to change the optical path length difference.

FIG. 11 is a diagram showing the results of plotting the relationship between the optical path length difference and the visibility of the interference image. Visibility means the magnitude of the contrast between the light and dark of the interference fringes. The plot points were approximated by a Gaussian curve, and the optical path length difference in which the visibility was 1 / e of the peak value was defined as the coherence length a. In the example shown in FIG. 11, the coherence length a = 26 μm was calculated.

(Measurement method of waveguide distance)
Hereinafter, an example of a method for measuring the waveguide distance b will be described.

FIG. 12 is a diagram schematically showing an example of a measurement system. As the light source 1201, a laser having a sufficiently long coherence length a of, for example, 1 m or more as compared with the expected waveguide distance b is used. The laser is, for example, a continuously oscillated single-mode DFB laser.

The retardation sample 1202 is formed with the same recesses as the retardation sample 82 used in the above-described embodiment. The depth of the depression is set so that the difference in brightness in the detected image is maximized. The depth corresponds to, for example, a phase difference of 180 degrees.

An image is formed on the image pickup apparatus 1204 by the lens optical system 1203. A detected image is obtained by the above-mentioned arithmetic processing. Instead of the image pickup device 1204, as shown in FIG. 8, the light transmitted through the optical element 84 including the light-shielding film 9 and the optical coupling layer 12 may be observed with a microscope.

FIG. 13 is a diagram showing the result of plotting the relationship between the distance and the brightness in the detected image. In the example shown in FIG. 13, the luminance averaged in the Y direction in the detected image is plotted along the X direction. The distance is zero at the point where the brightness averaged in the Y direction is the darkest. The brightness is standardized with the darkest value being 1 and the brightest value being zero. The plot points were approximated by an exponential function, and the distance at which the brightness became 1 / e of the peak value was defined as the waveguide distance b. In the example shown in FIG. 13, the waveguide distance b = 18 μm was calculated.

The imaging device in the present disclosure can be applied to measurement for industrial use, medical use, beauty use, security use, in-vehicle use, and the like. Further, for example, a new imaging function such as a phase distribution or a coherence distribution can be added to a digital still camera or a video camera.

100 Imaging System 1, 81, 1001, 1201 Light Source
2 Subject
3, 83, 1203 Lens optics 4, 1004, 1204, 1401 Imaging device 5 Incident light 9 Light-shielding film 9a, 1402a Opening 9A, 1402A Light-shielding part 10, 1404 Light detector 10a, 1404a First light detector 10A, 1404A Second light detector 11a First microlens 11a Second microlens 12, 1403 Optical coupling layer 82, 1202 Phase difference sample 84 Optical element 1005a, 1005b Mirror 1006 Half mirror

Claims (8)

An optical coupling layer that includes a grating and guides the light when light of a predetermined wavelength and a predetermined angle of incidence is incident.
A plurality of photodetectors arranged under the optical coupling layer, having an imaging surface, and periodically arranged along the imaging surface.
With
Let the coherence length of the light be a [μm].
The waveguide distance of light that is guided in the optical coupling layer along the direction in which the grating has a period is b [μm].
When the period of the plurality of photodetectors is p [μm],

Meet,
Imaging device. A light-shielding film arranged on the photobonding layer is provided.
The plurality of photodetectors include a plurality of first photodetectors and a plurality of second photodetectors.
The light-shielding film includes a plurality of alternately arranged openings and a plurality of light-shielding portions.
The plurality of openings face each of the plurality of first photodetectors, and the plurality of openings face each other.
The plurality of light-shielding portions face each of the plurality of second photodetectors, respectively.

Meet,
The imaging device according to claim 1. The optical coupling layer is placed on the first low refractive index layer, the first high refractive index layer arranged on the first low refractive index layer and containing the grating, and on the first high refractive index layer. Including a second low index layer arranged
The first high refractive index layer has a higher refractive index than the first low refractive index layer and the second low refractive index layer.
The imaging device according to claim 1 or 2. The coherence length of light is

Meet,
The imaging device according to any one of claims 1 to 3. The coherence length of light is

Meet,
The imaging device according to any one of claims 1 to 3. The plurality of photodetectors are arranged two-dimensionally.
The imaging device according to any one of claims 1 to 5. The light incident on the optical coupling layer contains a component of TM polarized light.
The imaging device according to any one of claims 1 to 6. The imaging device according to any one of claims 1 to 7.
A light source that emits the light having a coherence length a and
To prepare
Imaging system.

Images